Epoxy resins are reactive compounds, e.g., monomers or, oligomers, and/or polymers that contain epoxide groups. Epoxy resins may be reacted, which can be referred to as cross-linking or curing, to form a cured material, such as a cured coating. These cured materials are desirable for some applications due to improved mechanical properties and/or improved chemical resistance as compared to some other materials.
For some coating applications, epoxy resins that yield a cured coating with a relatively low crosslink density that can improve flexibility, adhesion, and/or impact resistance are desirable. This can be important on articles that flex, such as metal structures (e.g., bridges, storage tanks, vehicles). Some diglycidyl ether based coatings are not useful for these applications, as they can have a high crosslink density and are used on rigid substrates such as those made of concrete.
To achieve cured coatings with lower crosslink densities, higher molecular weight epoxy resins can be used. However, when higher molecular weight epoxy resins are crosslinked through terminal epoxy groups, there is a greater distance between crosslink points than for lower molecular weight liquid epoxy resins. The higher molecular weight epoxy resins can have a viscosity that results in challenges associated with applicability (e.g., the high molecular weight epoxy resin can be too viscous to be applied as desired).
The viscosity of the epoxy resin can be reduced through viscosity reducing techniques that use solvents, diluents, and/or heated application equipment. However, use of solvents (e.g., xylene) is not always desirable, as they are considered volatile organic compounds (VOCs), as they evaporate when used. Use of diluents, such as organic compounds with active hydrogens (e.g., benzyl alcohol) or epoxy functional compounds such as cresol glycidyl ether or butanediol diglycidyl ether, can be incompletely reacted into the epoxy coating during cure, resulting in VOCs and/or deteriorization in properties in the final coating due to disruption of crosslinking and/or plasticization. Heated application equipment, which can also be utilized to reduce viscosity, can be impractical due to costs associated with acquisition and maintenance.
Without the use of added solvents, diluents, and/or heated application equipment, however, the epoxy resin may have a viscosity that is too high for application. It is therefore desirable to provide a higher molecular weight epoxy resin with a lower viscosity to reduce use of solvents, diluents, and/or heated application equipment, for example.